JPH10285951A - Transformer for inverter output circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized transformer for an output without generating DC biased magnetization at all, and to provide the transformer for the inverter output, in which a maximum difficult point is solved. SOLUTION: In dependent symmetric top transformer 1 and transformer 2 in a magnetic circuit are used, the two transformers are employed as the positive half-wave exclusive transformer 1 and the negative half-wave exclusive transformer, primary windings 1P and 2P, secondary windings 1S and 2S and tertiary windings 1T and 2T flowing DC are installed to the transformer 1 and the transformer 2, an DC current, by which the core magnetic flux density of the transformer 1 and the transformer 2 is placed at positive and negative saturation points, is flowed through the tertiary windings at all times and DC biased magnetization is eliminated, and loads are halved by operation only of positive or negative half waves in each transformer, and the transformers can be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an inverter output circuit, and more particularly to a transformer connected to an inverter output circuit.

[0002]

2. Description of the Related Art An inverter is a device that converts direct current into alternating current by switching a direct current by a semiconductor switching element such as a transistor or a thyristor. However, when an inverter output circuit has a transformer, slight variations in switching timing occur. Also, the positive and negative AC output waveforms cannot be made symmetrical due to variations in the characteristics of the switching elements. Due to the difference between the positive and negative waveforms, the inverter circuit transformer causes DC bias.

FIG. 6 is an output circuit diagram of a conventional push-pull type center tap type inverter, showing an example in which a transistor is used as a switching element.

[0004] In FIG. 6, INV is an inverter circuit, the inverter circuit INV consists transistor Q _A and the transistor Q _B, connects the emitters of the transistor Q _B of the transistor Q _A, a DC power source connection point It is connected to the negative side of the E _a.

[0005] positive output transformer 3 of the DC power source E _A
Of being connected to the neutral point N of the primary winding 3P, the emitter of the collector of the transistor Q _B of the transistor Q _A is connected to both ends of the primary winding 3P of the transformer 3 for the output. Thus, the primary winding 3P of the output transformer 3 is of the center tap type. The load L ₀ is connected to both ends of the secondary winding 3S transformer 3 for output.

The operation is such that the transistors Q _A and Q _B are alternately turned on and off so that DC currents of different directions flow through the two windings divided by the neutral point N of the primary winding 3 P,
The AC power is output to the secondary winding 3S.

[0007] Figure 7 is a inverter output circuit diagram of the conventional single phase full bridge circuit, in FIG. 7, the inverter circuit INV constitute a bridge circuit by the transistor Q _C, Q _D, Q _E and Q _F, a DC power source positive side of E _B is connected to the connection point between the collectors of the transistors Q _E of the transistor Q _C, the negative side of the DC power source E _B is connected to the connection point of the emitters of the transistors Q _F of the transistor Q _D Have been. Is connected to the collector of the emitter and the transistor Q _D of the transistor Q _C, this connection point is connected to one end of the primary winding 4P output transformer 4. Further, the emitter of the transistor Q _{E and} the collector of the transistor Q _F are connected to each other and to the other end of the primary winding 4 P of the output transformer 4. The load L ₀ is connected to both ends of the secondary winding 4S of the transformer 4 for output.

[0008] operation, the transistor Q _C and Q _F and Q _E
And a pair Q _D, turns on the transistor of pairs alternately by off control, to obtain an AC output to the secondary winding 4S by passing a different direction of the DC current in the primary winding 4P.

[0009]

6 and 7 described above.
In the case of the inverter output circuit transformer shown in (1), the positive and negative AC output waveforms cannot be made symmetric due to slight variations in switching timing and variations in characteristics of switching elements. Due to the difference between the positive and negative waveforms, the output transformer has a drawback of causing DC bias.

As a countermeasure to prevent this DC bias, conventionally, for the core of the transformer for the inverter output circuit, a material having a large core loss which is hard to cause a bias or a gap is provided in the core magnetic circuit to increase the exciting current. And make it hard to be demagnetized. For this reason, the transformer applied to the inverter output circuit has problems such as a large loss and a large noise when a gap is provided.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and provides a small-sized output transformer which does not cause DC bias at all. It is an object of the present invention to provide an inverter output transformer that solves the greatest difficulty of a transformer.

[0012]

In the present invention, a means for solving the above-mentioned problem is that a transformer used for an inverter output circuit is replaced with an identical transformer independent of a magnetic circuit.
Using a table, each transformer has a primary winding connected to the inverter output circuit, a secondary winding connected to the load, and a tertiary winding for passing DC, and the tertiary winding of one of the transformers The lines
A DC current is applied to place the core magnetic flux density of the transformer at the positive saturation point, and a DC current is applied to the tertiary winding of the other transformer to place the core magnetic flux density of the transformer at the negative saturation point.

As described above, the magnetic flux density of the iron core is brought to one magnetic saturation point (waving), and the magnetic flux density is always changed from this point as a starting point in one direction so that magnetic saturation does not occur. . Also, two units require a pair of transformers, but only one positive or negative half-wave flows per unit, so the capacity per unit is about half and the iron core is small,
A small-sized inverter output circuit transformer with no magnetic bias is obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

FIG. 1 is a circuit diagram showing an example of application of a first embodiment of an inverter output transformer to a push-pull circuit according to the present invention. It is characterized by using transformers 1 and 2 having the same (symmetric) transformer independent of circuits.

In FIG. 1, INV denotes an inverter circuit. The inverter circuit INV includes transistors Q ₁ and Q ₂ whose emitters are connected to each other, and these transistors Q ₁ and Q _2.
1, consisting of respectively parallel connected diodes D ₁ and D ₂ to Q _2. The anodes of the diodes D ₁ and D ₂ are connected to the emitters of the transistors Q ₁ and Q ₂ . E is a direct current power supply, C ₁ denotes a capacitor connected in parallel to the DC power source E.

Each of the independent transformers 1 and 2 of the magnetic circuit has a primary winding 1P and 2P and a secondary winding 1P, respectively.
S and 2S, and tertiary windings 1T and 2T for DC magnetization.

One ends of primary windings 1P and 2P of transformers 1 and 2 are connected to the positive side of DC power supply E, and the other ends are connected to collectors of transistors Q ₁ and Q ₂ , respectively. , The negative side of the DC power supply E is
Connected to the emitter side of transistors Q ₁ and Q ₂ .

L ₀ is a load, and an AC output is supplied from the secondary windings 1S and 2S of the transformers 1 and 2 connected in series.

FIG. 1 shows an example in which the transformer 1 is used as a transformer dedicated to the positive half-wave, and the transformer 2 is used as a transformer dedicated to the negative half-wave. The tertiary winding 1T of the transformer 1 is When there is no input to the primary winding 1P of the heater 1, the magnetization of the iron core is changed to the negative saturation point -B _S
And the tertiary winding 2T of the transformer 2 is
This is a winding for setting the magnetization of the iron core to a positive saturation point + B _S when there is no input to the primary winding 2P of the transformer 2. Therefore, a DC current I for magnetization is continuously supplied to the respective tertiary windings 1T and 2T.

FIG. 2 is a BH curve diagram showing the magnetizing characteristics of the iron core of the first transformer. As shown in FIG. 2, the magnetizing characteristics of the transformer 1 are negative with no input to the primary winding 1P. At the time of a half-wave, the magnetizing force −H _S is given to the iron core by the DC current I flowing through the tertiary winding 1T, and the iron core magnetic flux density becomes a negative saturation point −B _S (point A).
It has become. When a positive half-wave voltage is applied to the primary winding 1P, the magnetization characteristics of the iron core form a hysteresis loop of A → B → H → D → E → F → A. The maximum magnetic flux density at the two points + _Bh is a value corresponding to the time product of the input voltage. B _h is designed to be lower than the magnetic saturation point.

FIG. 3 is a BH curve diagram showing the magnetization characteristics of the iron core of the second transformer. As shown in FIG. 3, the magnetization characteristics of the transformer 2 have a positive value with no input to the primary winding 2P. when half-wave, the magnetizing force by the DC current I flowing through the tertiary winding 2T + H _S is applied to the core, the core flux density is positive saturation point + B _S (i '
Point). And the voltage of the negative half wave is the primary winding 2
When applied to P, the magnetization characteristics of this iron core are
Draw a hysteresis loop of C ′ → D ′ → E ′ → F ′ → A ′. The maximum magnetic flux density -B _h of two 'points are set to values corresponding to time product of the input voltage. B _h is designed to be lower than the magnetic saturation point.

As described above, the change in the magnetic flux density of the transformer core of the present invention is about twice as small as the saturation magnetic flux density of the iron core material. On the other hand, there is a difference that the change in the magnetic flux density of the conventional transformer changes symmetrically to + B _h and −B _h starting from almost zero.

Since the magnetic flux density of the core of the transformer is shifted to one magnetic saturation point and is always changed in one direction from this point, the design value of the magnetic flux density of the core is reduced to less than twice the saturation magnetic flux density. Very little magnetic saturation occurs.

FIG. 4 is a circuit diagram showing a DC magnetizing circuit for supplying a DC current to a tertiary winding in an embodiment of a transformer for an inverter output circuit according to the present invention. DC current source E _S is connected to tertiary winding 1T via reactor L. Reactor L is for blocking alternating component voltage appearing at the tertiary winding 1T against the DC power source E _S side. Note that R _V indicates a current regulator.

FIG. 5 is a circuit diagram showing a second embodiment of the present invention, showing an application example in which the inverter circuit INV is formed by a single-phase full bridge circuit.

In FIG. 5, the inverter INV forms a bridge circuit by transistors Q ₃ , Q ₄ , Q ₅ and Q ₆ as switching elements, and the positive side of the DC power source E is connected to the collector of the transistor Q ₃ and the transistor Q _{3. 5} is connected to the collector, the negative side of the DC power source E is connected to the emitters of the transistor Q ₆ of the transistor Q _4. The emitter and collector of the transistor Q ₆ of the transistor Q ₅ is connected, the connection line is connected to the cathode of the anode and the diode D ₄ of the diode D _3. The cathode of the diode D ₃ is connected to one end of the primary winding 1P of transformer 1, the anode of the diode D ₄ is connected to one end of the primary winding 2P of the transformer 2.

Further, it is connected to the emitter of the collector of the transistor Q ₃ of the transistor Q _4, and is connected to the primary winding 1P of transformer 1 and the other end of the primary winding 2P of the transformer 2.

In this case, the polarity between the primary winding 1P and the secondary winding 1S of the transformer 1 and the polarity between the primary winding 2P of the transformer 2 and the secondary winding 2S of the transformer 2 is connected to the load L ₀ is connected in parallel with opposite are connected to the polarity, the secondary winding 2S of the transformer secondary winding 1S and the transformer 2 and.

The transformer 1 is a transformer dedicated to the positive half-wave, and the transformer 2 is a transformer dedicated to the negative half-wave. In addition to the primary windings 1P and 2P and the secondary windings 1S and 2S, DC It has tertiary windings 1T and 2T for magnetization. Tertiary winding 1 of transformer 1
T is, when there is no input to the primary winding 1P of transformer 1, a winding for placing the magnetization of the iron core in negative saturation point -B _S, tertiary winding 2T of the transformer 2, the transformer 2 This is a winding for setting the magnetization of the iron core to the positive saturation point + B _S when there is no input to the primary winding 2P. Therefore, the DC current for magnetization is continuously supplied to the tertiary windings 1T and 2T as in the push-pull type inverter output circuit of the first embodiment.

Note that the magnetization characteristics of the core of each transformer are also the first.
Since it is the same as that of the push-pull type inverter output circuit of the embodiment and is the same as that shown in FIGS. 2 and 3, the description is omitted.

[0032]

The transformer for an inverter output circuit according to the present invention is composed of two identical transformers each having an independent magnetic circuit, and each of them is a transformer dedicated to a positive half-wave and a transformer dedicated to a negative half-wave. In addition to the primary winding connected to the inverter output circuit and the secondary winding connected to the load, a tertiary winding is provided, and the core magnetic flux density of this tertiary winding is set to a positive saturation point, and Since the DC current at the negative saturation point is configured to always flow, the following effects are obtained.

(1) The iron core of the conventional transformer for an inverter output circuit has a magnetic flux density change starting from near zero as a starting point.
If the zero point deviates, the magnetic field is immediately demagnetized.However, in the present invention, the magnetic flux density of the iron core of the transformer is shifted to one magnetic saturation point, and only this point is used as the starting point, and only the magnetic flux density is changed in one direction. Even if the magnetic flux density design value of the iron core is set to slightly less than twice the saturation magnetic flux density, magnetic saturation does not occur.

(2) The transformer for an inverter output circuit of the present invention requires two pairs of transformers, but each unit operates only a positive half-wave or a negative half-wave, and the duty is 1 /. 2. For this reason, the capacity per unit is half of the conventional capacity.
Further, even if the magnetic flux density of the iron core is set to the full saturation point, there is no fear of saturation, and the iron core becomes small.

(3) As a whole, it is possible to provide a transformer which does not cause any magnetic demagnetization without increasing the size as compared with the conventional one, and can solve the greatest difficulty of the conventional inverter output circuit transformer.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a first embodiment of a transformer for an inverter output circuit according to the present invention.

FIG. 2 is an excitation characteristic diagram showing an image of an excitation characteristic of an iron core of a positive half-wave transformer in an embodiment of a transformer for an inverter output circuit of the present invention.

FIG. 3 is an excitation characteristic diagram showing an image of an excitation characteristic of an iron core of a transformer for a negative half-wave in an embodiment of a transformer for an inverter output circuit of the present invention.

FIG. 4 is a circuit diagram showing a DC magnetizing circuit for flowing DC through a tertiary winding in the embodiment of the transformer for an inverter output circuit of the present invention.

FIG. 5 is a circuit configuration diagram of a second embodiment of an inverter output circuit transformer according to the present invention.

FIG. 6 is a circuit diagram showing an example of a conventional push-pull type inverter output circuit transformer circuit.

FIG. 7 is a circuit diagram showing an example of a conventional single-phase full-bridge type inverter output transformer circuit.

[Explanation of symbols]

1,2 ... output transformer 1P, 2P ... primary winding 1S of the output transformer, 2S ... secondary winding 1T of the output transformer, tertiary winding lines S ₁ of 2T ... output transformer, S ₂ ... capacitor _{D 1, D 2, D 3} , D 4, D 5, D 6 ... diode E ... DC power source E _S ... DC current source I ... DC current L ... reactor L ₀ ... load Q _1, Q _2, Q ₃ , Q ₄ , Q ₅ , Q ₆ ... switching elements (transistors)

Claims (1)

[Claims] 1. An output transformer applied to an inverter output circuit, wherein two identical and independent transformers of a magnetic circuit are used, each transformer including a primary winding connected to the inverter output circuit, A secondary winding connected to the load and a tertiary winding for direct current flow.The tertiary winding of one transformer has a positive saturation of the core magnetic flux density of the transformer when there is no input to the primary winding. A DC current is applied to the transformer, and a DC current is applied to the tertiary winding of the other transformer, which places the core magnetic flux density of the transformer at the negative saturation point when there is no input to the primary winding. Transformer for inverter output circuit.